There is thin provisioning, as capacity virtualization technology, which allows use of a volume exceeding the physical disk capacity. Thin provisioning allows efficient use of physical resources by managing physical disks collectively as a storage pool and allocating physical resources (capacity of physical disks) according to the amount of data written in a virtualized logical volume.
In addition, there is a technique of performing data backup while attempting to mitigate wasting of physical resources using this thin provisioning (for example, see Japanese Laid-open Patent Publication No. 2008-130080 and Japanese National Publication of International Patent Application No. 2008-547123).
In recent years, virtualized software which performs virtual control of a storage apparatus has been provided with a function capable of releasing physical resources from an area which has not been used since allocation of physical resources.
In addition, as a data backup method for a storage apparatus, there is known Copy-On-Write (COR). Copy-on-write is a function which allows reference to a copy source as it is without copying to a copy destination logical volume even when a copy request is issued, and which performs a copy to the copy destination logical volume when updating data of the copy source. Using such a copy-on-write function mitigates waste of physical resources due to copy processes.
However, immediately releasing physical resources allocated to a copy source logical volume according to a release command of physical resources in a storage apparatus that uses a backup method such as the copy-on-write function may cause the logical volume to lose data stored in the physical resources to be released, since copying to the copy destination logical volume has not yet been performed.
In order to cope with such a data loss, it is desired to allocate physical resources to the copy destination logical volume and save data therein. It may take substantial time until completion of the data saving process depending on the data size, and the physical resource release command may result in a command time-out.